The present invention relates generally to thermal decomposition apparatus for thermally decomposing various wastes which contain general wastes including polymers of resins, industrial wastes, infectious medical wastes, and chemical substances such as PCBs and waste oils without producing gas containing harmful substances.
In the current society, an enormous amount of wastes are discharged daily and their disposal is a great problem. The wastes include various kinds such as general, industrial and medical wastes. Most of the wastes are processed by burning or burial, which has several problems. The primary problem with the burning process is the production of harmful substances. In the burning process, the wastes are burned with air. Thus, harmful substances such as soot, dust, carbon monoxide and nitrogen compounds, such as NOx, are produced and discharged with other exhaust gas. Since the burning temperature is at about 700-800° C., harmful dioxin is produced and hence exhaust gas and ashes containing dioxin are produced.
The harmful substance content of the exhaust gas is regulated, especially substances such as dioxin, which has a very high toxicity and adversely affects human bodies for a long time.
In order to prevent production of dioxin, the following measures are available:
(1) The wastes which produce no dioxin are segregate from the ones which produce dioxin, and only the ones which produce no dioxin are burned;                (2) A device is used for removing dioxin contained in the exhaust gas discharged from an incinerator and is attached to an incinerator; or        (3) An incinerator which burns wastes at a high temperature such that dioxin is difficult to produce (hereinafter referred to as a high temperature incinerator) is used.        
There is, however, the problem with the first method in that it takes time and costs considerably more to segregate the wastes. In addition, it is substantially impossible to perfectly separate the wastes and production of a small amount of dioxin cannot be avoided.
The second method is insufficient to cope with dioxin because there are presently no devices capable of completely removing dioxin. Thus, it is insufficient to cope with dioxin. Thus, a secondary incinerator is required for burning dioxin contained in the exhaust gas, a cooling device for rapidly cooling the exhaust gas so as not to reproduce dioxin, and a filter for removing dioxin remaining in the exhaust gas is installed on the incinerator. However, installation of such devices in combination is costly and renders a more complicated incinerator.
As described above, the exhaust gas contains a plurality of harmful substances in addition to dioxin. In order to eliminate them all, a plurality of devices for removing such harmful substances are required to be attached to the incinerator. Thus, the incinerator would become expensive and complicated in structure.
Since the high temperature incinerator is expensive, there is a problem with the third method that it is not easy to replace the old incinerator with a new high temperature incinerator. In addition, it is difficult to completely prevent production of even a small amount of dioxin even with the high temperature incinerator.
Burning the wastes also has problems other than production of the harmful substances. Usually, wastes contain incombustible substances such as metals and glass. Therefore, when the wastes are burned, incombustible materials are produced and required to be removed from the incinerator, which takes much time. In terms of time and cost, it is difficult to segregate the wastes according to material type and then to process the different material types separately.
In addition, there are wastes which contain substantial amounts of incombustible materials, such as industrial wastes and shredder dust, including the remains of car bodies and household appliances. These wastes are not suitable for burning.
The other method for processing wastes is burial. It is becoming increasingly difficult to secure a place where the wastes are to be buried. In addition, there is the problem that chemical substances contained in the wastes will react when buried to resynthesize new chemical (harmful) substances. Furthermore, harmful heavy metals such as lead and/or harmful chemical substances such as dioxin contained in the wastes dissolve in rain to pollute the soil, rivers and ground water (soil pollution, water pollution) and thereby destroy the environment.
Methods appropriate (efficient and safe) for disposal of certain kinds of the wastes, such as PCBs and/or dioxin, have not yet been found and hence these wastes can only be stored and kept. Such wastes may leak out during their storage to pollute the environment and hence further measures are required to be taken.
In order to solve the above various problems, an apparatus capable of disposing of all wastes without producing harmful substances are desired, for example, an apparatus for thermally decomposing the wastes at high temperatures without burning them. However, it is difficult to efficiently obtain high temperatures to thermally decompose all the wastes.
It is therefore an object of the present invention to provide inexpensive thermal decomposition apparatuses for wastes which solve the above problems and which thermally decomposes wastes without producing harmful substances such as soot, dust, chlorine compounds such as hydrogen chloride, nitrogen compounds such as NOx and/or dioxin.